Known methods for forming conductive patterns of conductive circuits, electrodes, or the like used for touch panels, electronic paper, and various electronic components are a printing method and an etching method.
In a case of employing the etching method to form a conductive pattern, it is necessary to form a patterned resist film by photolithography on various metal films deposited on a substrate, subsequently to dissolve and remove unnecessary portions of the deposited metal films in a chemical or electrochemical manner, and finally to remove the resist film. Thus, the steps are very complicated and are not suitable for mass production.
On the other hand, in a case of employing the printing method, desired patterns can be mass-produced at low cost and printed films are dried or cured to thereby easily acquire conductivity. Such printing processes include flexographic printing, screen printing, gravure printing, gravure offset printing, inkjet printing, and the like, which have been proposed in accordance with the line width, thickness, or production speed of the pattern to be formed. Recently, from the viewpoint of, for example, size reduction of electronic devices and improvements in design, there is a demand for a fine conductive pattern formed by printing and having, for example, a line width of 50 μm or less, which is difficult to print by commonly used screen printing.
In addition, in order to meet an increasing demand for reduction in the thickness and weight of electronic devices and for flexible electronic devices and in order to employ highly productive roll-to-roll printing, there is a demand for a conductive paste that is applied to a plastic film by printing and is fired at low temperature for a short period of time to thereby achieve high conductivity, adhesion to the substrate, film hardness, and the like. In addition, there is a demand for a conductive paste that provides such properties when the conductive paste is applied by printing to printing objects such as, among plastic films, inexpensive and highly transparent PET films and transparent conductive films having ITO films on PET films.
From such a viewpoint, for the purpose of obtaining finer conductive patterns at higher productivity, among the above-described various printing processes, instead of the screen printing process, the gravure offset printing process is attracting attention. The gravure offset printing process is employed to print a fine wiring pattern by using a gravure plate having a recess that corresponds to image lines and is to be filled with a paste, a doctor configured to fill the recess of the gravure plate with the paste, a blanket cylinder to which the paste is transferred from the recess of the gravure plate, and a press cylinder disposed so as to face the blanket cylinder such that printing objects are supplied between the press cylinder and the blanket cylinder.
Known examples of such a method in which a conductive paste containing a resin component is used, printing is performed on a printing object by the gravure offset printing process, and firing is performed to form a conductive pattern, include methods of using resins that are themselves solid at 50° C. such as polyester resins, acrylic resins, epoxy resins, and ethyl cellulose (refer to Patent Literatures 1 and 2); and methods of using such resins in combination with resins that are liquid at 50° C. such as oxetane-based resins, epoxy-based resins, or vinyl-ether-based monomers (refer to Patent Literature 3).
However, such gravure plates used in Patent Literatures (PTLs) 1 to 3 have linear recesses to be filled with paste and do not have what is called bezel-pattern recesses, which are used for actual electronic components and are constituted by two or more linear recesses connected together so as to have, for example, a regular L shape, an inverted L shape, a U-shape rotated 90° anticlockwise, a U-shape rotated 90° clockwise, or a square-frame shape.
PTL 1: Japanese Unexamined Patent Application Publication No. 2010-159350
PTL 2: Japanese Unexamined Patent Application Publication No. 2010-235780
PTL 3: Japanese Unexamined Patent Application Publication No. 2011-37999